The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Some embodiments relate to methods applied to a well bore penetrating a subterranean formation, and more particularly, methods for zonal isolation.
Hydrocarbons (oil, condensate, and gas) are typically produced from wells that are drilled into the formations containing them. For a variety of reasons, such as inherently low permeability of the reservoirs or damage to the formation caused by drilling and completion of the well, the flow of hydrocarbons into the well is undesirably low. In this case, the well is “stimulated” for example using hydraulic fracturing, chemical (usually acid) stimulation, or a combination of the two (called acid fracturing or fracture acidizing).
In hydraulic and acid fracturing, a first, viscous fluid called the pad is typically injected into the formation to initiate and propagate the fracture. This is followed by a second fluid that contains a proppant to keep the fracture open after the pumping pressure is released. Granular proppant materials may include sand, ceramic beads, or other materials. These types of materials are well known to those skilled in the art. In “acid” fracturing, the second fluid contains an acid or other chemical such as a chelating agent that can dissolve part of the rock, causing irregular etching of the fracture face and removal of some of the mineral matter, resulting in the fracture not completely closing when the pumping is stopped. Occasionally, hydraulic fracturing can be done without a highly viscosified fluid (i.e., slick water) to minimize the damage caused by polymers or the cost of other viscosifiers.
Hydraulic and acid fracturing of horizontal wells as well as multi-layered formations frequently requires using diverting techniques in order to enable fracturing redirection between different zones. The list of these diverting methods includes, but not limited to, using mechanical isolation devises such as packers and well bore plugs, setting bridge plugs, pumping ball sealers, pumping slurred benzoic acid flakes and removable/degradable particulates. As well, other treatment may require use of diverting techniques.
Treatment diversion with particulates is typically based on bridging of particles of the diverting material behind casing and forming a plug by accumulating the rest of the particles at the formed bridge. Several typical problems related to treatment diversion with particulate materials are: reducing bridging ability of diverting slurry during pumping because of dilution with well bore fluid (interface mixing), necessity of using relatively large amount of diverting materials, and poor stability of some diverting agents during pumping and during subsequent treatment stage.
On the other way, during the drilling of a well bore, various fluids are typically used in the well for a variety of functions. The fluids may be circulated through a drill pipe and drill bit into the well bore, and then may subsequently flow upward through the well bore to the surface. During this circulation, the drilling fluid may act to remove drill cuttings from the bottom of the hole to the surface, to suspend cuttings and weighting material when circulation is interrupted, to control subsurface pressures, to maintain the integrity of the well bore until the well section is cased and cemented, to isolate the fluids from the formation by providing sufficient hydrostatic pressure to prevent the ingress of formation fluids into the well bore, to cool and lubricate the drill string and bit, and/or to maximize penetration rate.
Lost circulation is a recurring drilling problem, characterized by loss of drilling mud into downhole formations. It can occur naturally in formations that are fractured, highly permeable, porous, cavernous, or vugular. These earth formations can include shale, sands, gravel, shell beds, reef deposits, limestone, dolomite, and chalk, among others. Other problems encountered while drilling and producing oil and gas include stuck pipe, hole collapse, loss of well control, and loss of or decreased production.
Lost circulation is frequently controlled by including an additive in fluids injected into well bores. The most common additive used to control or cease lost circulation is bentonite which will seal small holes or fractures. Bentonite, in higher concentrations, increases viscosity and slows the fluid flow into the surrounding rock. Other solids, such as ground paper, ground corn cobs and sawdust, have also been used to control fluid loss. Polymers are also sometimes used to increase the viscosity of a well bore fluid and to control fluid loss. Polymer additives, however, are generally more expensive than particulates such as bentonite.
Methods disclosed herewith offer a new way to create diverting techniques, zonal isolation or techniques thereof.